Circuit for controlling the resonance frequency of an oscillatory circuit



p 1960 G. ROSIER ETAL 2,951,995

CIRCUIT FOR CUNTROLLING THE RESONANCE FREQUENCY OF AN OSCILLATORYCIRCUIT Filed Sept. 16, 1957 Ilu loo

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Fl 6.5 \1 g Fl INVENTOR GERARDUS QOSIER MARIE MARCEL ANTOINE ARNOLDGHISLAIN VERSTRAELEN BY la) AGEN 2,951,995 Patented Sept. 6, 1960 UnitedStates Patent CIRCUIT FOR CONTROLLING THE RESONANCE FREQUENCY OF ANOSCILLATORY CIRCUIT Gerardus Rosier and Marie Marcel Antoine -ArnoldGhislain Verstraelen, both of Hilversum, Netherlands, assignors to NorthAmerican Philips Company, Inc., New York, N.Y., a corporation ofDelaware Filed Sept. 16, 1957, Ser. No. 684,177 Claims priority,application Netherlands a. 2, 1956 5Claims. (21. 332-16 In suchcircuits, use is made of the variable time duringwhich the rectifier isconducting as a function of the control value in said seriescombination, so that the current flowing through the series combination,which is shifted in phase with respect to the voltage of the circuit, isvaried by the control value and hence causes the reso- Enance of thecircuit to be detuned.

In most cases, a control voltage is included as a variable .thresholdvoltage in series with the rectifier, but this has :the disadvantagewith respect to a control current to be :supplied to the rectifier thatthe resultant detuning is ;greatly dependent upon the ratio between thevoltage of 1 the circuit and the control voltage, whilst in practice itis :also very difiicult to obtain a linear relationship between thedetuning obtained and the control voltage. However, when use is made ofa control current, a considerably Ihigher control energy is required,unless the control source is connected to the rectifier via a choke coilwhich is active for the frequency of the circuit, but the choke coilwith said capacitor then introduces unwanted addittional resonance.

The invention is characterized in that the collector base path of atransistor is connected as a rectifier, whilst the control value issupplied to the emitter-base circuit. Ht underlies recognition of thefact that the collector-base circuit of the transistor operates, inco-action with the capacitor, as a detector for the voltage of thecircuit and produces a corresponding voltage at the collector of thetransistor, which voltage is active as a supply voltage for thetransistor. The alternating current traversing said series-combinationis, in this case, substantial-1y proportional to the emitter-controlcurrent of the transistor, whilst only a small control energy isrequired.

in this connection, it is mentioned that circuits for detuning a circuitby means of a transistor are known per se, which transistor is notconnected as a collectorbase rectifier, but is normally connected as anamplifier .and coupled to the circuit via a capacitor constituting an:impedance, negligible, for example, for the frequency of the circuit.In this case, the circuit is detuned by the finner collector-basecapacity or in general the inner collector base impedance of thetransistor which is dependent upon the emitter current. However, thevariation in capacity or impedance with the emitter current is far frombeing linear and also applies only for a much restricted Lregion.

In order that the invention may be readily carried into e'ifect, it willnow be described more fully, by way of example, with reference to theaccompanying drawing, in which:

Fig. 1 shows one embodiment of the invention;

Fig. 2 shows voltage-time and current-time diagrams which servetoexplain Fig. 1;

Fig. 3 shows a variant of Fig. 1;

Fig. 4 shows another variant of Fig. 1;

Fig. 5 shows a variant of Fig. 1 comprising a transistor of specialtype; and

Fig. 6 shows voltage-time and current-time diagrams to explain Fig. 5.Referring now to Fig. 1, the oscillatory circuit to be detuned isindicated by 1. It may be included in a feedback circuit comprisingtransistors 2 and 3, so that undamped oscillations are maintained acrossthe circuit 1. For controlling the resonance frequency of the circuit 1and hence the frequency of the oscillations produced, said circuithascoupled to it a detector circuit comprising the series-combination of acapacitor 4 and the collector-base path of a transistor 5 which isactive as a rectifier, the transistor being assumed to be of the p-n-ptype. Said frequency is controlled by a control voltage supplied viaterminals 6 to the emitter of transistor 5.

If the emitter current I of transistor 5 is zero, it will show, due tocollector-base rectification, a collector voltage V as a function of thetime t, as shown in Fig. 2A. This voltage has, on the average, aconsiderable negative value and may thus serve as the biassing potentialrequired to operate transistor 5 as an amplifier. If, therefore, anemitter current I is supplied to the terminals 6,

this current reaches the collector of transistor 5 and charges theright-hand electrode of capacitor 4 in positive sense resulting in avoltage-time diagram as shown in Fig. 2B (curve shown in full line).

During the transient positive peaks of the collector voltage V in Fig.23, a current i flows due to collectorbase rectification (Fig. 2C) andduring the longer negative periods, there is a flow of currentsubstantially equal to the control current L, which is supplied to theterminals 6. Since the collector has no direct-current connection withthe other electrodes, the voltage V adjusts itself in a manner such thatthe current i does not contain a direct-current component. Analternating voltage is then set up across the capacitor 4, which voltageis obtained by integration of the current i and is equal to thesinusoidal voltage across the circuit 1 (curve shown in dotted line inFig. 2B) and the actually produced collector voltage V (curve shown infull line in Fig. 2B). The fundamental wave of the alternating current iproduced is then found to be substantially proportional to the emittercontrol-current 1 so that linear frequency modulation becomes possiblethrough a wide range. The modulation energy required for this purpose isthen extremely small.

Several variations of the circuit shown in Fig. 1 are possible. Thus, inFig. 3, the control voltage may alternatively be included as ahigh-ohmic voltage source 7 in the base circuit of transistor 5. The RCfilter 8 must in this case have a small impedance for the circuitfrequency with respect to the impedance of capacitor 4, but a highimpedance for the frequencies of the source 7.

Furthermore, instead of utilizing a current source or a voltage source,use may be made of a radiation source, for example a small lamp 9 (Fig.4), as the source of control voltage. The load carriers thus released inthe emitter-base junction bring about quite similarpheofthe-base-material-hasbeen-removed-byetching,--resuiting in a smallgroove 16. -For a voltage V at the collector g: such that the depletionlayer starting frorn this collecter and penetrating the' base gone *breaches a a groove 16, the current path between emitter leand basecontact b is interrupted.

If such a transistor is-connectedyiaeapaeiterq tg gthe oscillatorycircuit l in' the/manner shown inFig. l,-wl1ilst a modulation source 6is included in the=emitter-cirgxih the collector'voltage' V and-"thecollector current i each show, as a function of time, an image asshown-infliigs. -6A -and-'6B,' respectively. "The collector current icutoff atthe moment wherr "the-collector voltage V frea'ches the valueVThe current-i is'thus-- sh ilfted in phase substantially exactly 90--w-ith'respectto the voltage Y -so that the circuit- 1- is gdarnped;toasmaller extent;

What is claimed is: V I

1. A circuit for-controlling the resonant frequency of an oscillatorycircuit-comprising atransistor-havingbase, collector, and emitter;electrodes, a capacitor-having one terminal comprising thesole'connection to said collector electrode, means connecting said-baseelectrode and the other terminal of said capacitor-to different pointsonsaid oscillatory circuit; and means applying a control voltage to theemitter-base circuit of; said transistor. I

2. A circuit for-controlling the1'resonant'freqnency 9f an oscillatorycircuit comprising a transistor having base, collector, andemitterelectrodes, a capacitor haying one terminal comprising the solecqnnection to said collector -electrode, means connecting said baseelectrode and the other terminal of said capacitor to difierent; pointson said oscillatory circuit so that acollector electrode voltage isprovided as aresult of collector-baserectification of oscillationsapplied to the collector-base path of said transistor by way of; saidcapaciton; animeans; applying a control voltage to the emitter-basecircuit of said tran--sistertovary-the-phaseef"said-eolleetonelectrode-voltage and therebydetune said oseillatory circuit.

3. A circuit as claimed in claim 2, in which said transistor isresponsive to radiant epergy, and in which said means applying a controlvoltage to the emitter-base circu t-stea .tta sistpr Tsasa scams cf-radan eaergy- ,4. .flfiimuikaspclaim m ;claim12,;-in which said; tran-.istqr.i thety ein uhi fihe u e fl wi bet e theaat tte laa lba le trelss: iat r untedawh n lectotl asthma-e ectrode xweds a pcadetena aedtxae- 5. A frequency modulation system comprising an 0s cillator having afrequency determining-circuit, a transiste h t n haseaso lee qr, an emte -ele ro e a capacitor connected serially between one point of saidfrequency determining-circuit and said collector electrode andcomprising the sole connection to said collector electrode,nieanscOIgneeting-said base electrode to another point ensaid frequencYdetermining circuit so that a collectpr voltage is provided as a resultof collector-base rectification, and a source ofcontrol-yoltageconnected bet-ween said base-and emitter --electrodes.

References Gited in -thej file of this patent UNlTEDaSTAIE VPAI NT:2;6\66,'9 02 rKoros -Jan.' 19, $1954 72,164,687 i-tBuchanan et a1 Sept-25, 195.6 12fi78;956 :Daceyetal 12111522,: 1957 2,790,088 ShiveApr.:'23,1l=95'7 1233051397 zlkoss Sept. 13,4957 2,8443795 ti-Ierring'Iuly;22,.'195.8

.EEQREIGNiPAIEN-IS lg-13 1 428 France Feb. '21; 1957 x, fir

